[OE-core][RFC PATCH 03/08] kernel-devsrc: add build and source PACKAGECONFIG levels

[bruce.ashfield@gmail.com]

From: Bruce Ashfield <bruce.ashfield@gmail.com>

Debugging the kernel from a debug rootfs needs its source at
/usr/src/kernel, where the debug info points, but kernel-devsrc only
carries what is needed to build modules, and installing it pulls in the
build tools (bc, bison, flex, gcc-plugins, openssl-dev, ...).

Split the content of the one kernel-devsrc tree into PACKAGECONFIG
levels instead of adding a second source package:

  build:  today's content and RDEPENDS ('make scripts prepare' on
          target). The default, so nothing changes for existing users.
  source: a curated spine (KERNELDEV_SOURCE_SPINE plus arch/${ARCH})
          and the drivers/sound files the kernel build read, taken from
          the kernel's kernel-source-files manifest. Only source files
          are copied, never scripts, so there are no runtime or file
          dependencies.

The RDEPENDS are split out, so they are only added when the 'build'
level is enabled.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
---
 meta/recipes-kernel/linux/kernel-devsrc.bb | 107 +++++++++++++++------
 1 file changed, 80 insertions(+), 27 deletions(-)

diff --git a/meta/recipes-kernel/linux/kernel-devsrc.bb b/meta/recipes-kernel/linux/kernel-devsrc.bb
index 90bdbfc534..3b83fd145c 100644
--- a/meta/recipes-kernel/linux/kernel-devsrc.bb
+++ b/meta/recipes-kernel/linux/kernel-devsrc.bb
@@ -28,30 +28,31 @@ B = "${STAGING_KERNEL_BUILDDIR}"
 
 PACKAGE_ARCH = "${MACHINE_ARCH}"
 
+# The flags choose what goes in the kernel-devsrc tree:
+#   build:  what is needed to build out of tree modules against the kernel
+#           ('make scripts prepare' on target). The default, and what
+#           kernel-devsrc has always been.
+#   source: the source needed to debug a kernel built for a specific
+#           MACHINE, see KERNELDEV_SOURCE_SPINE. No runtime dependencies,
+#           so it can go in a debug rootfs without the build tools.
+PACKAGECONFIG ?= "build"
+PACKAGECONFIG[build] = ",,,${KERNELDEV_BUILD_RDEPENDS}"
+PACKAGECONFIG[source] = ",,"
+
+# The curated part of the 'source' level, copied in full along with
+# arch/${ARCH}. The rest (drivers, sound, samples, ...) is not curated: the
+# files the kernel build read are discovered from the manifest the kernel
+# stages in do_shared_workdir. The manifest could find the spine's files too,
+# but the spine is listed so that 'source' always has a sane default.
+KERNELDEV_SOURCE_SPINE ?= "block certs crypto fs include init io_uring ipc kernel lib mm net security virt"
+
 KERNEL_BUILD_ROOT = "${nonarch_base_libdir}/modules/"
 
-do_install() {
+# The 'build' level: what is needed to build out of tree modules against the
+# kernel ('make scripts prepare' on target), and what kernel-devsrc has
+# always contained.
+kernel_devsrc_install_build() {
     kerneldir=${D}${KERNEL_BUILD_ROOT}${KERNEL_VERSION}
-    install -d $kerneldir
-
-    # create the directory structure
-    rm -f $kerneldir/build
-    rm -f $kerneldir/source
-    mkdir -p $kerneldir/build
-
-    # for compatibility with some older variants of this package, we
-    # create  a /usr/src/kernel symlink to /lib/modules/<version>/source
-    mkdir -p ${D}/usr/src
-    (
-        cd ${D}/usr/src
-        ln -rs ${D}${KERNEL_BUILD_ROOT}${KERNEL_VERSION}/source kernel
-    )
-
-    # for on target purposes, we unify build and source
-    (
-        cd $kerneldir
-        ln -s build source
-    )
 
     # first copy everything
     (
@@ -448,7 +449,58 @@ do_install() {
         sed -i 's,/usr/bin/env python2,/usr/bin/env python3,' "$ss"
         sed -i 's,/usr/bin/python$,/usr/bin/env python3,' "$ss"
     done
+}
+
+# The 'source' level: the curated spine plus the files the kernel build read,
+# from the manifest the kernel stages in do_shared_workdir. Only source files
+# are copied, never scripts, so the package gets no interpreter dependencies.
+kernel_devsrc_install_source() {
+    kerneldir=${D}${KERNEL_BUILD_ROOT}${KERNEL_VERSION}
 
+    if [ ! -s ${B}/kernel-source-files ]; then
+        bbfatal "${B}/kernel-source-files is missing, the kernel did not stage its source manifest"
+    fi
+    (
+        cd ${S}
+        {
+            find ${KERNELDEV_SOURCE_SPINE} arch/${ARCH} -type f
+            cat ${B}/kernel-source-files
+        } | grep -E '\.([chS]|rs)$' | sort -u | cpio --quiet -pdlu $kerneldir/build
+    )
+}
+
+do_install() {
+    kerneldir=${D}${KERNEL_BUILD_ROOT}${KERNEL_VERSION}
+    install -d $kerneldir
+
+    # create the directory structure
+    rm -f $kerneldir/build
+    rm -f $kerneldir/source
+    mkdir -p $kerneldir/build
+
+    # for compatibility with some older variants of this package, we
+    # create  a /usr/src/kernel symlink to /lib/modules/<version>/source
+    mkdir -p ${D}/usr/src
+    (
+        cd ${D}/usr/src
+        ln -rs ${D}${KERNEL_BUILD_ROOT}${KERNEL_VERSION}/source kernel
+    )
+
+    # for on target purposes, we unify build and source
+    (
+        cd $kerneldir
+        ln -s build source
+    )
+
+    if [ -n "${@bb.utils.contains('PACKAGECONFIG', 'build', '1', '', d)}" ]; then
+        kernel_devsrc_install_build
+    fi
+
+    # The 'source' level goes in the same tree, at /usr/src/kernel, which is
+    # where the kernel's debug info points.
+    if [ -n "${@bb.utils.contains('PACKAGECONFIG', 'source', '1', '', d)}" ]; then
+        kernel_devsrc_install_source
+    fi
     chown -R root:root ${D}
 }
 
@@ -457,14 +509,15 @@ do_install[lockfiles] = "${TMPDIR}/kernel-scripts.lock"
 
 FILES:${PN} = "${KERNEL_BUILD_ROOT} ${KERNEL_SRC_PATH}"
 
-RDEPENDS:${PN} = "bc python3-core flex bison ${TCLIBC}-utils gawk"
+# Added to RDEPENDS:${PN} by the 'build' PACKAGECONFIG
+KERNELDEV_BUILD_RDEPENDS = "bc python3-core flex bison ${TCLIBC}-utils gawk"
 # 4.15+ needs these next two RDEPENDS
-RDEPENDS:${PN} += "openssl-dev util-linux"
+KERNELDEV_BUILD_RDEPENDS += "openssl-dev util-linux"
 # and x86 needs a bit more for 4.15+
-RDEPENDS:${PN} += "${@bb.utils.contains('ARCH', 'x86', 'elfutils-dev', '', d)}"
+KERNELDEV_BUILD_RDEPENDS += "${@bb.utils.contains('ARCH', 'x86', 'elfutils-dev', '', d)}"
 # powerpc needs elfutils on 6.3+
-RDEPENDS:${PN} += "${@bb.utils.contains('ARCH', 'powerpc', 'elfutils-dev', '', d)}"
+KERNELDEV_BUILD_RDEPENDS += "${@bb.utils.contains('ARCH', 'powerpc', 'elfutils-dev', '', d)}"
 # 5.8+ needs gcc-plugins libmpc-dev
-RDEPENDS:${PN} += "gcc-plugins libmpc-dev"
+KERNELDEV_BUILD_RDEPENDS += "gcc-plugins libmpc-dev"
 # 5.13+ needs grep for powerpc
-RDEPENDS:${PN}:append:powerpc = " grep"
+KERNELDEV_BUILD_RDEPENDS:append:powerpc = " grep"
-- 
2.43.0